Large-scale droughts/ floods and monsoon circulation.

An objective numerical drought index based on monthly monsoon rainfall and duration has been developed for assessment of drought intensity. The drought intensity equation serves the dual purpose of assessing the intensity of drought as well as flood. The Drought Area Index (DAI) is defined as the percentage area of India having a mean monsoon index ≤ −2 (i.e., moderate or higher drought severity). Likewise, the Flood Area Index (FAI) is the percentage area of India with mean monsoon index ≥ +2 (i.e., moderate or more severe wetness), where the mean monsoon index is the mean drought index for the four monsoon months. A year is defined as a large-scale drought or flood year when DAI or FAI ≥ 25. Using the evolved criteria, years of large-scale drought and flood over India have been identified during the period 1891–1975. The method adopted for defining large-scale drought or flood does bear out the actual experience. Power spectrum analysis reveals a weak triennial cycle in DAI series and a highly significant quasi-periodicity of 20 years in the FAI series—nearly a double sunspot cycle. The FAI series is in phase with the double sunspot cycle and large-scale floods have been more frequent in the high-amplitude maximum phase of sunspot cycle. Weaker meridional pressure gradients, larger northward seasonal shifts of the monsoon trough, larger numbers of days of breaks in the monsoon, smaller frequencies of depressions and shorter westward extents of depression tracks appear to be the major factors associated with large-scale droughts, opposite features have been observed for large-scale floods. The height of the 200 mb surface in May is found to be abnormally low in the latitude belt 15–30°N, along 70°E during large-scale drought years, in contrast to abnormally high levels during flood years. The 200 mb surface during May seems to have the potential for prediction of extreme abnormality in the following monsoon season

Changes in the pattern of distribution of southwest monsoon rainfall over India associated with sunspots

Despite the systematic nature of the monsoon rains over India, large year-to-year variations in the pattern of distribution of rainfall during the season occur. The yearly pattern of rainfall distribution during the monsoon season (May 31–October 2) for each of the years 1901–51 for a network of 105 stations over India is characterized by a set of six distribution parameters. A brief description of the spatial distribution of the different patterns is given to indicate the nature of the component patterns. Polynomial trend analyses of the time series of the distribution parameters indicate oscillatory features. Power spectrum analyses reveal certain significant periods corresponding to the sunspot cycle or some higher harmonics with regional preferences. The variation of distribution parameters in the different parts of the country with the different sunspot epochs is demonstrated. Studies of the distribution of surface pressure anomalies, frequency of storms and depressions, and the frequency of “breaks in monsoon” associated with the contrasting sunspot epochs suggest that the monsoon circulation features as well as the characteristics of the rainfall distribution have a periodicity nearing the sunspot cycle

Oscillations of a monsoon system Pt.I Observational aspects

In this paper the elements of a monsoon system are defined, and its oscillations are determined from spectral analysis of long observational records. The elements of the monsoon system include pressure of the monsoon trough, pressure of the Mascarene high, cross-equatorial low-level jet, Tibetan high, tropical easterly jet, monsoon cloud cover, monsoon rainfall, dry static stability of the lower troposphere, and moist static stability of the lower troposphere. The summer monsoon months over India during normal monsoon rainfall years are considered as guidelines in the selection of data for the period of this study. The salient result of this study is that there seems to exist a quasi-biweekly oscillation in almost all of the elements of the monsoon system. For some of these elements, such as the surface pressure field, monsoon rainfall, low-level cross-equatorial jet and monsoon cloudiness, the amplitude of this oscillation in quasi-biweekly range is very pronounced. For the spectral representation of the time series, the product of the spectral density times frequency is used as the ordinate and the log of the frequency as the abscissa. Dominant modes are also found in the shorter time scales (<6 days). A sequential ordering of elements of the monsoon systems for the quasi-biweekly oscillation is carried out in terms of their respective phase angle. The principal result here is that soon after the maximum dry and moist static instabilities are realized in the stabilizing phase, there occur in sequence an intensification of the monsoon trough, satellite brightness, Mascarene high, Tibetan high and the tropical easterly jet. Soon after that the rainfall maximum over central India, arising primarily from monsoon depressions, is found to be a maximum

Solar activity and Indian weather/climate

The literature on influences of solar activity on the Indian weather and climate is reviewed since the discovery of sunspot cycle. Fluctuations in solar activity are undoubtedly a factor affecting weather and climate. Although the results of some of the studies are conflicting, Indian weather and climate is, in general, inversely related to sunspots. However, the areal extent of floods in India seems to expand and contract in phase with the Hale double sunspot cycle, suggesting that the flood rhythm is in some manner controlled by long-term solar activity related to solar magnetic effects. All the evidences of solar influences on weather and climate may have practical implications in improving long-range forecasting of weather and climate, once the physical coupling mechanisms and their modification by other factors are clearly understood. Some of the promising plausible physical mechanisms for explaining solar effects on weather and climate are also discussed

Systematic review with meta-analysis: Endoscopic balloon dilatation for Crohn's disease strictures

Background: Endoscopic balloon dilatation (EBD) is recognised treatment for symptomatic Crohn's strictures. Several case series report its efficacy. A systematic analysis for overall efficacy can inform the design of future studies. Aim: To examine symptomatic (SR) and technical response (TR) and adverse events (AE) of EBD. Stricture characteristics were also explored. Methods: A systematic search strategy of COCHRANE, MEDLINE and EMBASE was performed. All original studies reporting outcomes of EBD for Crohn's strictures were included. SR was defined as obstructive symptom-free outcome at the end of follow-up, TR as post-dilatation passage of the endoscope through a stricture, and adverse event as the presence of complication (perforation and/or bleeding). Pooled event rates across studies were expressed with summative statistics. Results: Twenty-five studies included 1089 patients and 2664 dilatations. Pooled event rates for SR, TR, complications and perforations were 70.2% (95% CI: 60-78.8%), 90.6% (95% CI: 87.8-92.8%), 6.4% (95% CI: 5.0-8.2) and 3% (95% CI: 2.2-4.0%) respectively. Cumulative surgery rate at 5 year follow-up was 75%. Pooled unweighted TR, SR, complication, perforation and surgery rates were 84%, 45%, 15%, 9% and 21% for de novo and 84%, 58%, 22%, 5% and 32% for anastomotic strictures. Outcomes between two stricture types were no different on subgroup meta-analysis. Conclusions: Efficacy and complication rates for endoscopic balloon dilatation were higher than previously reported. From the few studies with 5 year follow-up the majority required surgery. Future studies are needed to determine whether endoscopic balloon dilatation has significant long-term benefits